#include <signal.h>

void (*sigset(int sig, void (*handler)(int)))(int)
{
    struct sigaction sa, sa_old;
    sigset_t mask, mask_old;

    sigemptyset(&mask);
    if (sigaddset(&mask, sig) < 0)
        return SIG_ERR;
    
    if (handler == SIG_HOLD) {
        if (sigaction(sig, 0, &sa_old) < 0)
            return SIG_ERR;
        if (sigprocmask(SIG_BLOCK, &mask, &mask_old) < 0)
            return SIG_ERR;
    } else {
        sa.sa_handler = handler;
        sa.sa_flags = 0;
        sigemptyset(&sa.sa_mask);
        if (sigaction(sig, &sa, &sa_old) < 0)
            return SIG_ERR;
        if (sigprocmask(SIG_UNBLOCK, &mask, &mask_old) < 0)
            return SIG_ERR;
    }
    return sigismember(&mask_old, sig) ? SIG_HOLD : sa_old.sa_handler;
}
